Speed control for motive devices



May 25, 1948. c. MoTT Erm.

SPEED CONTROL FOR MOTIVE yDEVICES I Filed March '7, 1942 4 sheets-sheet 1 ATTORNEYS May 25,'1948. c. MoTT Erm.

SPEED CONTRO'L FOR MOTIVE DEVICES Filed March 7, 1942 4 Sheets-Sheet 2 am Rrwm or n E TomM N NMc. R unen m www. A mmm CMRY May 25, 1948. c. MoTT ETAL SPEED CONTROL FOR MOTIVE DEVICES Filed March '7, 1942 4 Sheets-Sheet' 5 www m@ 4 M NMeH. WMU n Ir R um, WA

CMRY

May 25, 1948.

c. MoTT ETAL y SPEED CONTROL FOR MOTIVE DEVICES Filed March 7, 1942 4 sheets-sheet INVENTOR CHESTER Marr 4u-Rza E caca/Aka Bisous/PT L. HARD/AG ATTORNEYS Patented Mey 25, 194s UNITED STATES PATENT OFFICE 2,442,013 SPEED CONTROL Foa Mo'rIvE DvIoEs Chester Mott, Evanston, and Alfred F. Chouinard and Robert L. Harding, Chicago, Ill., assignors to National Cylinder Gas Company, Chicago, Ill., a corporation of Delaware Application March 7, 1942, Serial No. 433,780

(Cl. S18-331) 9 Claims. 1 The present invention relates broadly to speed controls for motive devices, such as electric motors, hydraulic motors and air-driven motors. and more particularly to the use of such controls in torch cutting machines to control the rate of cutting. n h

Among the objects of the present invention is to provide a new and improved speed control den vice which (1) will operate through a wide range of speeds, (2) can be operated with extreme accuracy and within extremely narrow limits of speed variations at any selected speed, (3) per mits infinite gradual'changes in speeds within a predetermined range or xed step by step changes arranged in any desired series within said lrange, (4) permits quick changes in speed setting whether the controlled motive device is operatm ing or not, (5) permits positioning of the control device either near the motive device to be controlled or remote therefrom, (6) maintains constancy in speed setting, so that at any selected setting the motive device will always operate at a definite originally adjusted speed determined by. that setting, (7) utilizes such minute currents that the component parts of the, control device do not gradually deteriorate suiiiciently to affect the operation of said device, and

employs a thermionic valve or governor which deteriorates relatively suddenly, thereby making the necessity for replacement of said valve immediately apparent, (8) permits the stationary parte of the control device to form a self-.contained unit which can be electrically and mechanically connected to or disconnected from the movably controlled parts with ease and without the necessity of any skill, (9) can be easily attached to any 2 from one-eighth of an inch or less to twelve inches or more in thickness. In practice the rate of travel of the torch is not varied directly as the plate thickness, because the cut is necessarily wider for a thick plate than for a thin one, and it is common practice to use a larger tip size and a higher cutting oxygen pressure for thicker plates than for thin ones. Thus for a twelve-inch plate the rate of torch travel may be about oneseventh the rate of travel for a one-eighth inch plate because of the necessity of delivering a larger volume of oxygen per unit of time, or per unit of plate area to be out. Having determined the tip size and oxygen pressure needed for a plate of a given thickness, there is a deiinite speed of travel which should be imparted to the torch, and that speed should be kept constant. If it he too fast, the cut will not be completely through the plate; if it is too slow, an excessive amount of metal will be burned away, and the cut will be too wide; and if the speed varies, the cut will be irregular in width and the cut may be incomplete in places.

Another object is to provide a control device 2p of the type referred to for controlling the speed existing motive device to be controlled, (10) can he calibrated and operated to correlate any para vtisular data with any particular speed setting,

(11) allows the controlled motive device to den liver a torque at reduced speeds equal to its torque at maximum speed, and (12) is simple, comparatively inexpensive to manufacture and occupies a minimum amount of space.

In torch cutting machines, it is common practice to mount the @xy-acetylene cutting torch on a carriage, and to propel both the carriage and the torch along the carriage by an electric motor, which drives a traction wheel having guided movement in accordance with the path which it is desired to have the torch follow. For any given thickness .of plate of given composition, the rate of travel of the torch should be constant, but the speed of travel must be different lor plates of different thicknesses. Plates to be cut may vary' of the electricrnotor of the drive unit of a torch cutting machine to regulate the speed oi' cutting.

Various other objects, features and advantages of the invention will he apparent from the iol lowing particular description, and trom' an in@ spection ci the accompanying drawings, in which Fig. l is a somewhat simplified schematic diam gram .of a system incorporating the features of the' present invention, and showing the means by which the speed of a motive device, as riorl instance a direct current motor, can be selectivem ly controlled and changed, this system being shown with an alternating current generator for generating controlling voltage.

Fig. 1a is a portion of a somewhat simplied y schematic diagram of a system similar to that shown in Fig. 1, but showing the motor to be controlled, as for instance of the three phase type.

Fig. 1b is a portion of asomewhat simplified schematic diagram of a system similar to that shown in Fig. 1, but showing the motor to be controlled, as for instance of the hydraulic type.

Fig. 2'is a, more complete wiring diagram of the system shown in Fig. 1.

Eig. 3 is a portion of the wiring diagram of .a system employed when the generator for generating controlling voltage is of the direct current type. r

Fig. 4 is a perspective view somewhat diagrammatic showing a. torchcutting machine in corpoy of switch contact life.

rating the control features of the present invention.

Fig. 5 is a vertical somewhat schematic section of the torch cutting machine taken through the drive unit of said machine, and shown with the outer casing removed.

Fig. 6 is a horizontal section taken through the part of the torch cutting machine containing the motor speed control.

Fig. 7 is a front elevation of the part of the torch cutting machine containing the motor speed control, portions of the frame structure being shown broken away to reveal certain movable Darts oi.' said control.

Fig. 8 is a section taken on line 8-8 of Fig. 7, and

Fig. 9 is a face view of the control chart on the torch cutting machine used in commotion with the motor speed control device of the present invention.

In carrying out the features of the present invention, power, as-for example, electric current, is supplied to a motive device, such as an electric motor ID, for a period of time long enough to bring said motor to the desired speed of rotation. As soon as this motor I exceeds this speed, this current is automatically interrupted to cause said motorto slow down. When the motor I0 is slowed down below a certain speed, current ilow to the motor is automatically reestablished, so that the motor is again speeded up to the desired value. This cycle is repeated as long as the motor speed exceeds a maximum limit, and drops below a minimum limit. By making these two extreme operating limits narrow enough for any speed setting, the motor Ill can be made to operate with extreme accuracy and constancy at any selected speed.

In Fig. l is shown a simplified diagram of the manner in which the speed of the motor I0 can be controlled, the different parts being shown disproportionate for the sake of clarity, The motor I8 is supplied with current from the mains A, B, and is shown of the direct current type with a eld coil I i and an armature I2, although it may also be ci the alternating current type. Connected in series with this motor Eli are a variable resistance i3 and a relay switch i4, the switch and resistance being in parallel so that the reststance is cut out when the switch is opened. This relay switch I4 is needed for reducing or increasing the flow of current to said motor when said motor reaches maximum and minimum speed limits for ant,r setting ol the controis, The resistor i3, in conjunction with the condenser l performs the basic function of elimihating arcing at the contacts of relay switch Id. While the resistor I3 tends to establish a minimum speed of the motor when the relay switch ld is open, this action is not intentional and is reduced I y making resistor I3 variable to obtain a compromise between this minimum 'speed tendency and the maximum. arcing suppression; or resistor it can be open-circuited to entirely eliminate said tendency, with a consequent shortening The percentage of arc suppression, due to RC constant (resistance in ohms multiplied by capacitance in farads) established by the condenser i5 and the resistor it, approaches 100% with a decrease in resistor Iii up to a limit depending upon the motor speed. On the other hand, the minimum motor speed decreases with an increase in resistance at I3 to a point where the current flowing through the resistor is not of suiiicient value to operate the motor. Removing said resistor Il, leaving the circuit open at this point. has the same effect as increasing the resistance to an inilnite value. The motor armature I2 is mechanically coupled to a self-excited generator I6 either by direct connection as shown or by a belt or gear drive. When the switch I4 is closed, as shown in Fig l, the current flows from B through Il, wire a to point h and through I0, II and wire :f back to A. When the switch I4 is open, current flows from B along wire k, and a portion ol resistance Il to point h. and thence through Ill, II and i back to A.

.Although this generator I6 is shown comparatively large in the simplified diagram of Fig. 1, in actual practice this generator is comparatively small in size and electrical capacity, so that there is little or no loss of energy or slippage between the motor I0 and said generator, even if the two are belt connected.

Either an alternating current or a direct current generator may be used. The direct current generator may be one in which magnetic lines of force generated either by a field coil connected across its armature, or by a permanent magnet are cut by the rotating armature to generate direct current voltage. In the speciiic form shown, the generator I6 is of the alternating current self-excited type. and has a plurality of permanent magnets I'I (eight being shown) mounted for rotation with the armature shaft I8, and a. plurality of coils 20 (sixteen being shown) connected together in series and mounted on a stator, the alternating current generated in said coils being available at points 2I and 22.

The generated voltage available at points 2| and 22 varies directly with the speed of the generator armature, and this armature speed in turn is equal to the speedof the motor I0. It is therefore a simple matter to calculate the output peak voltage of the generator I6 at the points 2l and 22 at any speed once the maximum voltage at maximum speed is known.

Connected across the two points 2| and 22 in the output generator circuit is a resistor 23 having taps 24, 25 and 26 affording current at different voltages in accordance with the setting of a slider 2l. Although three taps are shown on the resistor` 23 to simplify explanation of the diagram of Fig. l, it must be understood that the number of resistor taps depends on the number of dierent speed settings desired. The resistor 23 may, if desired, be of the continuously variable type to allow for an infinite number of settings of the slider 2l which acts with the resistor as a selective potential divider.

The control voltage selected by the setting oi" the slider El is impressed on a thermionic valve or governor 30, to control the operation of the relay switch i4 in the motor circuit. This valve 30 is shown as a hot cathode gas tetrode having a cathode El, an. anode 32, a control grid. hetween said cathode and said anode, and a screen grid 3l! serving as a shield between said control grid and said anode, and also serving to reduce the interelectrode capacity within the tube. A filament 35 in the tube connected across the secondary coil of a transformer 3G serves to warm the cathode 3l, so that said cathode emits elec trons having a negative charge. The anode 32 has a positive potential connected to it, so that the electrons emitted by the cathode 3l will be attracted to said anode, Once this electron flow is created between the cathode 3i and the anode 32, a conductive circuit is established through the tube between these electrodes. A relay coil 31 controlling the switch I4 is connected to the circuit of the tube electrodes 3| and 32, so that when electron flow is established in the tube III between these electrodes, current will flow from main A' through relay coil 31 to anode 32, across the conductive path provided by the electron ilow to cathode 3|, to point 38 and then to the main B.

The grid 33 controlsthe electron flow passing therethrough. If this control grid 33 is sumciently negative in potential, it will repel the negative electrons from the cathode 3|. Any slight change below or above the critical potential of control grid 33 will actas a governing device for the iiow or stoppage of ilow of the electrons reaching anode 32. The tube 30 in the speciflc form shown is gas-filled, and designed for sharp cut-olf features, so that once anelectron ilow is established between cathode 3| and anode 32, the gas in the tube becomes ionized, and provides a greater conducting path and a larger number of free electrons than can be supplied by the hot cathode 3| alone. Furthermore, with this type of tube, at a certain value of potential on the anode 32, there is established a certain critical potential for the control grid 33, at which value the tube becomes conductive.

Another characteristic of these gas-illled tubes is that once plate current (i. e., electron ilow) is established, the grid 33 will not regain control by becoming more negative as long as there is a positive potential applied to anode plate 32. Consequently, the only way in which control may be returned to the grid 33 is by removing or reducing the potential at the anode 32. This is accomplished by applying at mains A', B' a source of alternating current, so that control is returned to the grid 33 sixty times a second, assumin-g that the current applied at these mains is sixty cycles.

A small battery 45 connected to the control grid lead 46 provides a. potential just suillclently negative to prevent the tube 30 from firing (i. e., establishing electron iiow) when no voltage is impressed at points 2| and 22 from the generator I6. A battery potential of approximately three volts is sufiicient for that purpose, and serves to prevent any current flow in the anode circuit when the generator I6 is not rotated, so that the relay coil 31 in said circuit is deenerglzed and the switch I 4 remains closed under spring action.

Upon rotation of the generator I6, avoltage generated thereby is impressed across points 2| andv22 of the resistor 23. With the slider 21 contacting tap point 26, the full generated voltage is applied across the tube input circuit at points 46 and 41. The negative side of the -battery 45 is connected to the lead 46 of the control grid 33, so that when the voltage delivered by the generator I6 approaches the constant voltage of constant magnitude delivered by said battery, and While the potential at point 2| resulting from the voltage generated by the unit I6 is positive during each cycle, the net-potential at that phase applied across the points 46 and 41 would be equal to the battery voltage minus the generated voltage. The net .potential would be lower than the critical voltage, below which the tube 30 fires. As soon as there is a'current flow in the anode circuit, relay coil 31 is energized and switch I4 is opened, so that current to the motor III is reduced and said motor slowed down. This causes a corresponding slowing down of the generator I6, so that the positive output potential at point 2| is decreased during each cycle ot the generated voltage, and the net potential applied at the tube input terminals 44 and 41 is increased. When this generated output positive potential is low enough so that the battery 46 delivers an increasing share of the net controlling voltage applied at points 46 and 41, and when this net voltage becomes greater than the critical ilrlng voltage required by tube 36, then the tube is extinguished (i. e., is prevented from carrying anode current through relay coil 31). Thus the switch I4 is closed and maximum current flow to the motor I0 reestablished. 'I'his causes the generator I6 to speed up until the net voltage at points 46 and 41 is again below the critical ring point of the tube 30. The original cycle of operation is then repeated.

The alternating current generatedby the unit I6 varies in frequency according to the armature speed of said unit. With eight magnets rotating with the armature shaft, the frequency of the generated current will be equal to eight cycles for every revolution per second. Assuming that the minimum operating speed of the motor I0 ls 500 R. P. M. or 8.33 revolutions per second, the frequency of the generated current at this minimum speed is about 66 cycles per second. With an alternating current generator I6, there results an opposition to the battery current only during the positive half of the cycle. Even at the slowest frequency generated of about 66 cycles per second, this frequency will be greater than the frequency (60 times per second) at which control is restored to the control grid 33 by the alternating current at the mains A', B'. The maximum lag in control is, therefore, no greater than l/to of a second when 60 cycles current is employed at the mains A', B. Therefore, as far as the degree of accuracy in control is concerned, it does not matter whether there is a D. C. or an A. C. potential applied to the control grid 33.

The tube 30 is fired or operated at one particular potential applied at its input terminals 46 and 41 irrespective of the total voltage generated by the unit I6 and made available at the points 2| and 22. Therefore, to obtain any control speed for the motor I0, the slider 21 is moved into position to contact any one of the tapped resistor points 24, 25 or 26. Since the potential between the point 2| and the slider 21 is equal to the potential applied to input terminals 46 and 41 of the tube 30, in order to obtain a tube ring potential at these terminals, it is necessary for the generator I6 to generate a much greater total voltage, so that the motor I0 must rotate at a greater speed, which speed is selected and determined by the setting of the slider 21.

As an example, assuming that the tube 30 is so designed that it will not conduct current in the anode circuit when a negative voltage of three volts is applied to the control grid 33, but when a negative potential of two volts is applied to said control grid, the tube 30 will fire. Also, assuming that the peak generated voltage for a generator speed of 500 R. P. M. is one volt, for 5,000 R. P. M. ten volts, and for 10,000 R. P. M. twenty volts, then with the slider 21 contacting resistor tap 26, the output peak voltage of the generator I6 amounting to one volt when the generator speed reaches 500 R. P. M. will be applied to points 2| and 41. During the positive half of the cycle of the generated voltage, this one volt in opposition to the three volts delivered by the battery 45 will cause a negative potential of two volts to be applied to points 46, 41. At this instant the tube 30 becomes conductive, so that flow of anode current is established, the relay 31 becomes energized and the switch I4 opened. The subsequent cycle of operation is as previously described to maintain the speed of the motor I|| at about 500 R. P. M.

With the slider 21 in contact with thetap 25, and assuming that the resistance between points 2| and 25 is 1/10 of the total resistance between points 2| and 26, then to obtain a value of one volt between points 2| and 41 it would be necessary for the generator I6 to generate a total peak voltage of ten volts before the tube 30 fires. To obtain this total voltage, the generator I6 must have a speed of 5,000 R. P. M. The one volt available between the points 2| and 41 resulting from a generator speed of 5,000 R. P. M. will, when algebraically added to the battery voltage of three volts, result in a net potential of two volts necessary to iire the tube, so that the speed of the motor I is maintained at about 5,000 R. P. M.

Assuming that the resistance between points 2| and 24 is 1/20 oi the total resistance between points 2| and 26, then when the slider 21 is set into contact with the tap 24, the Voltage applied at points 2| and 41 is one volt when a total positive peak voltage of twenty volts is generated by the generator I6. To obtain this voltage, the generator I6 must be driven at 10,000 R. P. M. For a setting of the slider 21 into contact with the resistor tap 24, the tube 30 operates in a manner already described to maintain the motor I0 at approximately a speed of 10,000 R. P. M.

The values of voltages specified in the above examples are not to be considered as the ones necessarily used in a practical arrangement. The examples imply that lthe tube 36 will not re at a potential of three volts and that it requires a full potential drop of one volt to fire the tube 36. As a matter of fact, the tube 30, in actual practice, can be operated on potential differences lower than 0.05 volt.

In Fig. la is shown a schematic simplified sys,- tem in which the motor I0a whose speed is to be controlled is of the three phase type. In this construction there are provided two resistors I3 in two of the phase circuits respectively and two corresponding switches I4 controlled from two relays 31 respectively. In all other respects the system is similar to that shown in Fig. l.

In Fig. 1b is shown a schematic simplified system in which the unit whose speed is to be controlled is a hydraulic Variable speed motor IIlb coupled to a generator (not shown). A solenoid valve I4b either on the inlet or outlet side of the motor Ib according to the nature of the motor, controls the ilow of actuating hydraulic fluid to said motor and thereby controls the speed of said motor. This Valve I4b is controlled by the solenoid 31h in the circuit of the thermlonic tube 30 in a manner already described with reference to the system of Fig. l. In all other respects the system of Fig. lb is similar to that shown in Fig. l.

As far as certain aspects of the invention are concerned, the unit whose speed is to be controlled may be a pump, a turbine, or other unit actuated by a lowable power agency.

In Fig. 2 is shown a more complete wiring diagram' of the speed control system shown in Fig. 1. In this system, the resistance I3 in the motor circuit reduces the voltage applied to the motor I6 when relay switch I4 is opened and thereby reduces the speed of said motor. This resistance I3 is shown tapped at three points 50, 5I and 52 to aiiox'd three values of resistance for the entire speed range of the motor I6, these values being picked by a rotary selector 5l comprising a contact ring 54, contacts 66 arranged and electrically interconnected into three series having electrical connections to the respective tapped resistance points 50, 5| and 52, and a pair of contact arms 60 and 6I connected to a shaft 62 and slidable over said contacts and said ring respectively. With this arrangement, the motor I0 for any speed setting will have one of three optimum speeds lower than the selected speed when relayswitch I4 is opened, but when the relay switch I4 is closed, full voltage is applied to the motor I0 and said motor tends to over-travel this selected speed. This is necessary to enable the motor II) to operate between the tolerance limits determined by the control circuit. This arrangement also serves to "over-voltage the motor l0 in order to supply any added torque when said motor is overloaded. The resistor I3, in combination with the condenser I5, performs the additional function of eliminating arcing at the contacts of relay switch I4.

The control is shown in Fig. 2 with thirty speed settings. The use of one resistor 23 for all oi these speed settings would be impractical, since it would be necessary for this resistor to be extremely long in order to maintain thirty taps thereon corresponding to these settings. For that purpose, there are provided fifteen resistors 23, each being utilized for two speed settings by tapping each resistor at two points 65 and 66, and connecting all thirty of these points to respective contacts 61 on the rotary selector 68. This selector 68 has a contact ring 10 and a pair of radial contact arms 1I and 'I2 slidable over said contacts and said ring respectively, and connected to the shaft |52 for rotation in unison with the contact arms 60 and 6Iv on the motor ballast selector 53.

For connecting into the control circuit the conductor leading to the resistor 23 picked by the selector 68, there is employed a third selector 15 havin-g a contact ring 11 and a series of contacts 16 corresponding in number to the contacts 61 on the selector 68. A pair of radial contact arms -I8 and 80 connected to shaft 62 slide over contacts 16 and ring 11 respectively.

The three selectors 53, 68 and 15 are operated in unison by rotation of the shaft 62, and are shown in Fig. 2 set into second motor speed position. In the operation of the system, alternating current supplied at mains A, B will iiow from line A to the primary coil of the transformer 36, so that the tube lament 35 is heated, and the tube made ready for operation. When the switch 82 is closed, current will iiow from main A to point 84, through motor relay switch I4 in closed position shown to point 85. From this point, the current continues through relay switch 86 in full line position shown, through motor armature I2, through relay switch 81 in full line position shown, and through the motor field II to main B. The switches 86 and 81 are operated in unison from a relay coil 88 into full or dotted line positions indicated in accordance with the desired direction of rotation of the motor I0.

With the generator I6 coupled to the motor I0, current during the position half of each cycle iiows from terminal 93 to point 94, through contact ring 11, through slide contact arms and 18 to the second selected contact 16, through the corresponding resistor 23 to points 95 and 96, and to the other terminal 91 of the generator I6.

From point 34, current also ows towards the positive side oi.' the battery 46 to buck the voltage of this battery, the negative side of the battery being connected through a grid current limiting resistor 98 to the control grid 33. The lower potential terminal for this bucking voltage is at point 65 on the selected resistor 23.

A fraction of the total voltage generated by the generator I6 and existing between the point |00 and 65 on the selected resistor 23, is applied between the terminals of the cathode 3| and the control grid 33. For that purpose, the circuit to the cathode 3| follows from point 65 to the second selected contact 61 on the selector 68, through the contact arms 1|l and 12, through the contact ring 10 to point |0I, and then to said cathode.

The voltage applied to the tube 30 between the terminals oi' the control grid 33 and the cathode 3| gradually increases the faster the generator I6 rotates. As soon as this voltage is high enough to buck the battery voltage which prevents the tube from firing, this tube will fire and become conductive, so that current will flow from the main A to point 84, through the relay 31 to the anode 32, through the electron stream to the cathode 3|, to points |0| and |02 to the main B. With the relay 31 energized, the switch |4 is opened, so that current iiow to the motor I is reduced. This causes the motor to slow down, so that the generator also slows down, and the voltage impressed on the tube 30 gradually decreased. When this generated voltage becomes low enough so that the battery 45-again gains control, the tube 30 is extinguished, platecurrent interrupted, and the relay 31 deenergized, so that the switch I4 is reclosed and the motor speeded up again.

s This cycle is repeated often enough, so that the average speed of the motor remains within an extremely narrow range of speeds.

The tube 30, the battery 45, transformer 36, switch |4 and the relay 31 are desirably mounted and enclosed in a cartridge |05, to form a selfcontained replaceable unit, which can be easily connected to or disconnected from the rest of the control system. To facilitate this connection or disconnection, the cartridge |05 is provided with a disconnect plug and socket |06 by which various conductors from the system outside of the cartridge may be plugged into electrical contact with the elements in said cartridge.

In Fig. 3 is shown a portion of the wiring diagram when the generator I6 is of the D. C. type.

In this diagram, point ||0 must always have a positive potential applied to it, and point must always have a negative potential. 'I'he D. C. generator I6 '(Fig. 3) reverses its polarities from thoseindicated at points 93 and 91 when its rotation is reversed in direction. Therefore, in order to provide for this change in direction of the generator without reversing the polarity of the points |'|0 and there is provided a pair of switches ||2 and ||3. These switches ||2 and ||3 are controlled from the relay 88 in unison with the switches 86 and 81, so that when the direction of the motor |0 is reversed, the switches I|2 and ||3 will be moved into position to maintain the proper polarity indicated for points ||0 and I.

As a feature of the present invention, the motor speed control shown and described is employed in a torch cutting machine to control the rate of cutting. As an example of the type of torch cutting machine in which the present invention may be employed, there is shown somewhat schematically in Figs. 4 and 5 a cutting apparatus having a carriage |20, which travels horizontally on rails over a table |2|, on which may be supported a templet, drawing, pattern or other guide. A drive unit |22, which may be of any well-known type, or which may be of the form shown and claimed in Patent 2,336,626, issued on copending application Serial' No. 395,616, is supported on carriage |20 for horizontal movement therealong crosswise o! the movement of said carriage. This drive unit |22 may, for instance, be supported for such movement along the carriage |20 by means of rollers |23 secured to the frame of the drive unit and engaging a pair of rails |24 on said carriage.

'I'he drive unit |22 has a tracing element |26 in the form of a tracer wheel, pointer, spot of light or the like, which can be steered along the outline of the pattern or other guide to be copied or traced. This tracing element |26 may be in the form of a traction wheel driven from the electric motor I0 forming part of the movable drive unit 22, or a separate traction wheel may be provided driven from said motor. In the form shown, the motor I0 is mounted on a turret |21, and drives the traction wheel |26 through a gear reduction unit |3| at one end ci a vertical shaft |30, and a gear train |28 at the other end of said shaft. The turret |21 rotates with the drive unit |22 in its steering movement, so that the motor |0 is correspondingly rotated as the traction wheel |26 is moved along the table |2|. As the drive unit |22 is steered over the table. it causes the movement of the carriage |20 along its rails, and movement of said unit along said carriage.

One or more torch units |33 are supported on the carriage |20, and are connected to the drive unit |22 by a bar |34 for movement therewith along said carriage and over the plate |35 to be cut, so that the cutting speed of these torch units corresponds to the speed of the traction wheel |26 and its directly connected drive motor |0. These torch units |33 may be of any suitable well-known construction, or may be of the form shown and claimed in Patent 2,336,596, issued on copending application Serial No. 378,102.

The generator I0, which generates the controlling voltage by which the speed o1 the motor I0 is regulated, is mounted on the turret |21 as shown in Fig. 5 with the armature of said generator connected directly to the armature shaft of the motor 0.

The change in speed of the motor 0 is effected automatically upon the setting of a cutting calculator chart device indexed with various plate thicknesses and mounted on carriage |20. This chart per se forms no part of the present invention, but is shown and claimed in copending application Serial No. 386,874, now Patent No. 2,364,644, dated December 21, 1944. This chart device indicatesvthe correct values and adjustments required for each particular thickness of plate being cut with a particular torch tip, and is adjustable to compensate for conditions which influence these values. For that purpose, the chart device comprises a lower stationary chart section |40 (Figs. 6, 7, 8 and 9), and an upper chart section |4| adjustably movable along the upper edge thereof, and provided with a horizontal row of figures indicating plate thicknesses. The lower chart section |40 4has a plurality of horizontal tabulations containing cutting data corresponding to respective plate thicknesses indicated in the upper chart section 4|. This data may include speed of torch travel in feet per l main pointer.

hour, or inches per minute, or feet per second or all three cutting tip sizes, cutting oxygen pressure and cubic feet of cutting oxygen consumed per foot of cut.

The proper cutting speed for a plate of a. definite thickness depends on the shape of the cut and various conditions of the plate. For instance, in making cuts having sharp corners,

beveis or curves, the speed of the cutting torch should be decreased. If the plate is warm, then the cutting speed should be increased. If cold, it should be decreased, and if the plate has a considerable amount of scale on its surface or is extra clean, the lineal cutting speed should be reduced or increased accordingly.

In order to adjust the chart device for these unusual conditions, there is provided on the upper chart section |4| a scale having an index or pointer 42, and the lower chart section |40 has a scale comprising a main pointer |43 and a series of auxiliary pointers |44 on opposite sides of said When the two pointers |42 and |43'` are in registry, the chart is set for normal plate conditions. By sliding the upper chart section |4| to effect registry of the pointer |42 with any one of the auxiliary pointers |44 in the lower chart section 40, the chart is corrected for abnormal conditions.

The slidable adjusting movement of the upper chart |4| may be effected through a handle |46 supported on the carriage |20 in accessible position for operation from the front of said carriage and secured to a suitably journalled shaft |45. This shaft |45 carries a forked arm |41 slidably receiving a pin |48 fixed to the upper chart section |4|.

An indicator slide |50 is movable across the face of the chart sections |40 and |4| into registry with that figure in the upper chart section |40 indicating the thickness of the plate to be cut, and is desirably in the form of a looped wire, which, when moved into registry with said figure, lines up and encloses the corresponding data in the lower chart section |40.

The movement of the indicator slide |50 across the face of the charts |40, |4| is effected from a hand wheel mounted on the carriage |20 and accessible for operation from the front of said carriage. The transmission between this hand wheel |5| and the slide |50 is shown comprising a bevel gear |52 mounted on the shaft |53 of the handle |5| and meshing with a bevel gear |54 secured to one end of a shaft |55. Near the other end of the shaft |55 is a pinion |56 meshing with a gear |51. which is mounted on the shaft 62. 'I'his shaft 62 carries a cable drum |60, the rotation of which is translated into lineal movement of the slide |50 over the charts |40, |4| by means of a cable |6| passing around said drum and over pulleys |62, |63 and |64. A slide block |65 carried by the cable |6| is connected to the upper end of the indicator slide 50, and is guided for slide movement by any suitable means, as, for instance. by the upper edge of a frame plate |66 extending with a free slide fit into a groove in the slide block |65, and forming an inclined backing plate for the charts |40, |4|. A spring |61 serves as a take-un for any slack that might develop in the cable |6|.

Although the cable is shown partially wound around the drum |60, it may be wound around said drum any number of revolutions. The relative position of the cable |6| with respect to the drum |60 may be fixed against slippage by a drum. Since the drum is made to rotate through a range of less than 360 for the full range of speeds, this fixed connection between the cable and the drum will not interfere with the proper operation of the indicating device.

The stationary contact parts of the three selector units 53. 68 and 15 are desirably formed into a single unit, and for that purpose are shown mounted on a single disc |10, with the three rows of contacts 55, 61 and 16 and the three solid contact rings 54, 10 and 11 concentrically mounted with respect to the axes of the control shaft 62. This speed control adjustment disc |10 is shown mounted on a bracket |1| having a rigid connection to the frame structure of the control housing |12, and has a central aperture to permit the passage of the control shaft 62 therethrough.

The three pairs of rotatable contact arms 60, 6|, 1|, 12, 18 and 80 are mounted on a disc |13, which is fixed to the gear |51 for rotation therewith by any suitable means, as for instance, the spacer sleeve |14 encircling the shaft 62.

When the hand Wheel |5| is turned to set the slide |50 on the chart |40 in accordance with the thickness of the plate to be cut, the control disc |13 is automatically set into proper contact position with the stationary control disc |10 to obtain the proper torch speed for said plate.

In order to insure the stopping of the rotary control disc |13 in proper contac-t position with respect to the stationary disc |10 for each speed setting, there is provided an index device which is shown comprising a sprocket |16 secured to the shaft and provided with a series of recesses |11 depending on the speed ratio between shafts |55 and 62. A roller |18 carried on a pawl |80 pivoted at |8| is urged against the periphery of the sprocket |16 by a spring |82. When the roller l|18 is in one of the cam recesses 11, the slide |50 will be in proper alignment with respect to the charts |40 and |4|, and the rotary control disc |13 will be in proper corresponding rotary contact position with respect to the stationary control disc |10. The two shafts |55 and 62 are so geared that successive positioning oi' the slide |50 will cause the snapping of the indexing roller |18 into successive sprocket recesses |11. The operator can tell when the proper setting has been reached by the feel of the control hand wheel I5 since it turns easily into correct position and offers greater resistance to turning as said hand wheel is moved out of correct position.

All of the control parts of the torch cutting machine are shown either mounted on or enclosed within the housing |12 mounted on the carriage |20 behind the front plate |83 of said carriage. The cartridge |05 containing the electrical parts shown in Fig. 2 rests on the floor of the housing |12, and is desirably provided with a handle |65 at one end to facilitate the insertion or removal of said cartridge into or out of said housing. The cartridge |05 has built therein one section |06a of the plug |06, as for instance, the male section, while the female plug section |06b nxed to the base of the housing |12 is mounted in position to electrically receive the male plug section when said cartridge is slipped into position in said housing.

Although the resistors 23 are not shown in Figs. 6, 7 and 8 for the sake of simplicity and clarity, these are mounted in any suitable position within the housing |12,

As many changes can be made in the above -method and apparatus, and many apparently screw (not shown) connecting said cable to said u widely different embodiments of this invention can be made without departing from the scope oi' the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What ls claimed is:

1. A speed regulating system for an electric motor, including an electric circuit for delivering electric current at full supply voltage to the motor, an independent circuit having means con- 'trilling the flow of current in said electric circuit,

and including a gas-filled electronic tube having motor, including an electric circuit for delivering anode and cathode elements in said control cirf cuit and a control grid element, means for irnpressing upon the control grid element a direct current voltage of constant magnitude and independent of the speed of the motor, and means for also impressing upon said contro] grid element a voltage, the frequency and magnitude of which vary with the speed ci the motor.

2. A speed regulating` system for an electric motor, including an electric circuit for delivering electric current at full supply voltage to the motor, an independent circuit having means ccntrolling the flow of current in said electric circuit, and including a gas-lled electronic tube having anode and cathode elements in said control cir-- cuit and a control grid element, a battery for impressing upon the control grid element a direct current voltage of constant magnitude, and means for also impressing upon said control grid element a voltage, the frequency and magnitude of which vary with the speed of the motor.

3. In combination, an electric motor of any variable speed type, a generator driven from said motor and generating a voltage depending in .value on the speed of said motor, a circuit including a hot gas-lled electronic tube having a cathode, an anode, and a control grid, means for impressing on said grid a direct current voltage of constant magnitude together with a selected proportion of the generated voltage to render said tube conductive when said impressed voltage exceeds a predetermined value, said tube being rendered non-conductive when said voltage drops below said predetermined value. a variable resistance across the output of said generator for selecting said proportion according to the desired motor speed, and means in the circuit of said motor, operated from said tube circuit, to prevent current ilow through said motor circuit when said tube becomes conductive,and to permit current flow at full supply voltage in said motor circuit when said tube becomes non-conductive, thereby maintaining said motor at the desired speed.

4. A speedy regulating system for an electric motor, including an electric circuit for delivering electric current at full supply voltage to the motor, an independent circuit having means controlling the iiow of current in said electric circuit, and including a gas-illled electronic tube having anode and cathode elements in said control circuit and a control grid element, means for impressing upon the control grid element a direct current voltage of constant magnitude and independent of the speed of the motor, and means for also impressing upon said control gridelement a selected proportion of a voltage the magnitude of which varies with the speed of the motor.

5. A speed regulating system for an electric motor, including an electric circuit for delivering electric current at full supplyvoltage to the motor, an independent circuit having means controlling the iiow of current in said electric circuit,

electric current at full supply voltage to the motor, an independent circuit having means controlling the flow of current in said electric circuit, and including a gas-filled electronic tube having anode and cathode elements in said control circuit and a control grid element, a battery for impressing upon the control grid element a direct current voltage of constant magnitude, and means for also impressing upon said control grid element a selected proportion of a, voltage, the magnitude of which varies with the speed of the motor.

7. An apparatus for controlling the speed of electric motor, comprising a circuit for delivering current at full supply voltage to said motor, means for generating a voltage in direct propornon to the speed of said motor, a potential divider for said generated voltage, means for generating a. direct current voltage of constant magnitude. an electronic tube, means for impressing on said electronic tube said direct current voltage Yand a portion said first mentioned voltage selected at said poteL-ital divider according to the vdesired speed of said motor, to stop and start current flow through said tube according to variations in said selected voltage,and means for controlling the flow of electric current to said motor in accordance with the flow of current through said tube.

8. Amapparatus for controlling the speed of an electric motor, comprising a circuit for delivering current at full supply voltage to said motor, an independent circuit including an electronic tube, means for generating a voltage in direct proportion tothe speed of the motor, a potential divider for said voltage, means for generating a direct current voltage of constant magnitude, means for impressing on said electronic tube said direct current voltage and the voltage delivered from said potential divider, and means in said/independent circuit for controlling the flow in said first mentioned circuit and thereby controlling the speed of the motor in accordance with the setting of said potential divider.

9. An apparatus for controlling the speed of an electric motor comprising a circuit for delivering full supply voltage current to said motor, means driven by said motor for generating a voltage depending in value upon the speed of said motor, an independent circuit having an electronic tube permitting or cutting off lull supply voltage current ow through said iirst mentioned circuit, means for impressing on said tube a direct current voltage of constant magnitude, means including a potential divider for impressing on said tube a selected proportion of said generated voltage, and means operated in accordance with they setting of said potential divider for varying the current ilow. to said motor.

' CHESTER MOT'I.

ALFRED F. CHOUINARD. ROBERT L. HARDING.

(References on following page) 15 REFERENCES CITED 16 Name Date Young Sept. 5, 1939 Bucknam Oct, 24, 1939 FOREIGN PATENTS Country Date Great Britain July 23, 1928 OTHER REFERENCES Handbook for Elec. Engis, Pender, First Edition, pages 1078-1079, published 1914 by John Wiley 8: Sons, New York, N. Y. 

